1. Field of the Invention
The main object of the invention is a processor to calculate the discrete Fourier transform, a processor comprising a real-time testing device.
The Fourier transform is an extremely powerful mathematical tool used especially to calculate spectra.
The Fourier transform can be used in particular to calculate convolution. For the Fourier transform of the convolution of two functions is equal to the Fourier transform product of these two functions. Thus, at each point, the convolution of two functions is equal to the reverse Fourier transform of the product of the Fourier transforms of these two functions.
It is often advantageous to weight a function for which it is desired to calculate the Fourier transform. The device, which is the object of the present invention, can be used to perform the weighting operation, upon command, for example before the calculation of the Fourier transform. For a discrete sequence, the weighting is done by multiplying the terms of the sequence by the weighting coefficients which are stored, for example, in a read-only memory. Advantageously, the read-only memory contains several sets of coefficients so that the desired weighting can be chosen.
It is often indispensable to verify the validity of the results calculated. This is especially important when a calculating device is used in a hostile environment. One solution lies, for example, in doubling the number of calculating circuits and in associating them with a comparator which validates the calculator only if the results calculated by both circuits are identical. This method proves to be very costly. The device according to the invention can be used to verify the results of the calculation of the Fourier transform for a pre-determined rate of error. For this, the device verifies the result of the calculation of the Fourier transform by means of Parseval's theorem. During a test, the circuit of the invention performs the calculation of Parseval. The result calculated by the operator is validated solely in case of equality of the two sides of Parseval's equation. The same processor can be used to calculate the Fourier transform and verify so that the complexity of the processor is not substantially increased.